Changing nomogram risk zone classification with serial testing after acute acetaminophen overdose: a retrospective database analysis.

CONTEXT: The Rumack-Matthew nomogram stratifies patients into discrete risk zones following acetaminophen (APAP) overdose. Treatment decisions have traditionally been based on the initial risk zone. "Line-crossing" between zones occurs and is poorly understood. The study objective was to characterize line-crossing behavior in acute APAP overdose patients, especially moving from below to above the nomogram treatment threshold. METHODS AND MATERIALS: The study was a secondary analysis of the Canadian Acetaminophen Overdose Study (CAOS) database, a large medical record review of patients hospitalized in eight large Canadian cities (1980-2005) following APAP poisoning. Population consisted of acute APAP overdose patients with at least two serum concentrations performed during hospitalization. Using ordinal logistic regression, we studied the effects of patient demographics, ingestion size/timing, APAP concentrations, time to N-acetylcysteine (NAC), and co-ingestants on a three-level dependent variable: patients whose risk increased two or more zones, those remaining in the same or adjacent zone, and those whose risk fell by two or more zones. RESULTS: Of the 3201 eligible hospitalizations with 7705 APAP concentrations, half (1679, 52.5%) crossed at least one zone (up or down) within 24 h of acute ingestion, including 190 (5.9%), who crossed at least two lines into a higher risk zone, and 516 (16.1%) at least two lines into a lower risk zone. Of the 1251 patients initially below the nomogram treatment line of 150 µg/mL, 131 (10.8%) patients crossed above this line. Being older, male, and co-ingesting opioids, antimuscarinics, or NSAIDs were independently associated with line-crossing. CONCLUSIONS: Patients commonly crossed nomogram risk zones, including from below to above the current treatment threshold. These findings support recommendations for serial APAP testing until the individual risk of hepatic injury is clearly established.

Can a serum acetaminophen concentration obtained less than 4 hours post-ingestion determine which patients do not require treatment with acetylcysteine?

CONTEXT: The interpretation of acetaminophen concentrations obtained prior to 4 hours after an acute, single overdose remains unclear. Patient care decisions in the Emergency Department could be accelerated if such concentrations could reliably exclude the need for treatment. OBJECTIVE: To determine the agreement between a serum acetaminophen concentration obtained less than 4 hours after an acute ingestion and the subsequent 4 + hour concentration, and the predictive accuracy of early concentrations for identifying patients with potentially toxic exposures. METHODS: A secondary analysis of patients admitted for acetaminophen poisoning at one of the 34 hospitals in eight Canadian cities from 1980 to 2005. We examined serum acetaminophen concentrations obtained less than 4 hours post-ingestion, and again 4 or more hours post-ingestion. For the diagnostic accuracy analysis, we specified a cutpoint of 100 µg/mL (662 µmol/L) obtained between 2 and 4 hours and a subsequent 4 to 20 hour acetaminophen concentration above the nomogram treatment line of 150 µg/mL (993 µmol/L). RESULTS: Of 2454 patients identified, 879 (36%) had a subsequent acetaminophen concentration above the nomogram treatment line. The 2-4 hour concentration demonstrated a sensitivity of 0.96 [95% CI; 0.94, 0.97] and a negative likelihood ratio of 0.070 [0.048, 0.10]. Coingested opioids reduced this sensitivity to 0.91 [0.83, 0.95], and antimuscarinics to 0.86 [0.72, 0.94]. Only very low to undetectable acetaminophen concentrations prior to 4 hours reliably excluded a subsequent concentration over the treatment line. CONCLUSIONS: Applying an acetaminophen concentration cutpoint of 100 µg/mL (662 µmol/L) at 2-4 hours after an acute ingestion as a threshold for repeat testing and/or treatment would occasionally miss potentially toxic exposures. Absorption of acetaminophen is only slightly delayed by coingested opioids or antimuscarinics. Our analysis validates the practice of not retesting when the first post-ingestion acetaminophen concentration is below the lower limit of quantification.

Outcomes of Patients With Premature Discontinuation of the 21-h Intravenous N-Acetylcysteine Protocol After Acute Acetaminophen Overdose.

BACKGROUND: The minimum recommended treatment duration for i.v. N-acetylcysteine (NAC) after an acute, single acetaminophen (APAP) overdose is 21 h. Some have questioned whether shorter courses may be sufficient in carefully selected cases. OBJECTIVE: We sought to describe the incidence of hepatotoxicity in a cohort of acute APAP overdose patients who received <21 h of i.v. NAC for any reason. METHODS: We performed a secondary analysis of a large multicenter retrospective cohort of patients hospitalized for APAP poisoning. We selected patients with a potentially toxic serum APAP concentration measured between 4 and 24 h post ingestion, in whom i.v. NAC was initiated but discontinued before completing the full 21-h course. We further characterized outcomes in these patients as a function of two novel risk-prediction tools, the psi (ψ) parameter and APAP × aminotransferase (AT) product. The ψ parameter is an estimate of the cellular burden of injury based on the area under the concentration-time curve before treatment, and calculated with respect to the APAP concentration and time to initiation of NAC. RESULTS: Fifty-nine patients met inclusion criteria. Intravenous NAC was initiated a median of 11.3 h post ingestion and administered for a median of 11.0 h. Hepatotoxicity (aspartate aminotransferase [AST] or alanine aminotransferase [ALT] > 1,000 IU/L) occurred in one patient (1.7%; 95% confidence interval 0.04-9.1), and eight additional patients developed hepatic injury (AST or ALT > 100 IU/L). No fatalities occurred. A multiplication product of APAP and AT (APAP × AT) that falls below 10,000 µmol/L/IU-L, or pretreatment ψ < 5 mmol/L-h suggested a low risk of hepatic injury. CONCLUSIONS: In this retrospective analysis of patients treated with < 21 h of i.v. NAC for acute APAP overdose, the incidence of hepatotoxicity and coagulopathy was low, despite delays to NAC treatment.

Effect of smoking on the pharmacokinetics of inhaled loxapine.

BACKGROUND: Loxapine inhalation powder delivered by a hand-held device as a thermally generated aerosol (ADASUVE) was recently approved in the United States and European Union for use in the acute treatment of agitation in patients with bipolar disorder or schizophrenia. As smokers comprise a large subpopulation of these patients, and many antipsychotic drugs require dose adjustments for smokers, the objective of this study was to compare the pharmacokinetics of inhaled loxapine administered to smokers and nonsmokers. METHODS: Pharmacokinetics and sedation pharmacodynamics using a visual analog scale were studied in 35 male and female adult subjects (18 nonsmokers and 17 smokers) following a single dose of 10 mg of inhaled loxapine. Blood samples were drawn at predose, 30 seconds, 1, 2, 3, 10, 30, and 60 minutes, and 2, 6, 12, and 24 hours after dosing. Loxapine and 8-OH-loxapine were analyzed using reverse-phase liquid chromatography coupled with a tandem mass spectrometer. Pharmacokinetic parameters assessed included Cmax, Tmax, AUCinf, and T1/2 for loxapine and 8-OH-loxapine. Geometric mean ratios (GMRs) were determined for smokers to nonsmokers. RESULTS: Loxapine Cmax was similar in smokers and nonsmokers with a GMR of 99.0%. The median loxapine Tmax was 1.88 and 1.01 minutes for nonsmokers and smokers, respectively. Loxapine AUCinf and AUClast values in nonsmokers were comparable with smokers (GMRs of 85.3% and 86.7%, respectively). A slight decrease in the observed mean terminal half-life values was observed for smokers (6.52 hours for smokers and 7.30 hours for nonsmokers). CONCLUSIONS: Sedation profiles and visual analog scale scores at each time point were similar for nonsmokers and smokers. It was concluded that inhaled loxapine does not require dosage adjustment based on smoking behavior.

Comparison of the 20-hour intravenous and 72-hour oral acetylcysteine protocols for the treatment of acute acetaminophen poisoning.

STUDY OBJECTIVE: To compare outcomes after acute acetaminophen poisoning in 2 large cohorts of patients treated with either the 20-hour intravenous or 72-hour oral acetylcysteine protocol. METHODS: We conducted a retrospective cohort study with historical control comparing patients treated with one of 2 acetylcysteine regimens. Data for the 20-hour group were obtained from a medical record review of patients on whom the 20-hour intravenous protocol was initiated in Canadian hospitals from 1980 to 2005. The 72-hour group consisted of a historical cohort of patients treated in US hospitals with the 72-hour oral protocol from 1976 to 1985. The primary outcome was hepatotoxicity (aminotransferase levels >1,000 IU/L). RESULTS: Of the 4,048 patients analyzed, 2,086 were in the 20-hour group and 1,962 were in the 72-hour group. The incidence of hepatotoxicity was 13.9% in the 20-hour group and 15.8% in the 72-hour group (-1.9% absolute difference; 95% confidence interval [CI] -4.2 to 0.3). The relative risk of hepatotoxicity was lower in the 20-hour group when acetylcysteine was initiated within 12 hours of ingestion. The relative risk was lower in the 72-hour group when acetylcysteine was initiated later than 18 hours after ingestion. There was no significant risk difference between groups when acetylcysteine treatment was started 12 to 18 hours after ingestion. One patient in the 20-hour group received a liver transplant and died because of acetaminophen toxicity compared with no liver transplants and 3 deaths in the 72-hour group. Anaphylactoid reactions to intravenous acetylcysteine were reported in 148 of 2,086 patients (7.1%; 95% CI 6.1% to 8.3%). This study is limited by comparison of 2 separate data sets from different countries and study years. CONCLUSION: The risk of hepatotoxicity differed between the 20-hour and 72-hour protocols according to the time to initiation of acetylcysteine. It favored the 20-hour protocol for patients presenting early and favored the 72-hour protocol for patients presenting late after acute acetaminophen overdose.